Hyperspectral electro-optical instruments or imaging spectrometers spread received light over an area array, and can be used in a “pushbroom” fashion to build up an image at a number of finely spaced wavelengths. Hyperspectral instruments, particularly wide field of view imaging spectrometers, are beginning to be seen as the instrument of choice on key future remote sensing programs. In the Earth Sciences, there are several proposed programs that require high performance infrared (IR) hyperspectral instruments. These include the Hyperspectral Environmental Suite (HES) on the Geostationary Operational Environmental Satellites (GOES), the Atmospheric Infrared Sounder (AIRS) and the Spaceborne Infrared Atmospheric Sounder for Geosynchronous Orbit (SIRAS-G) Instrument Incubator Program. Other proposed programs include atmospheric sounding instruments for Blue Horizons and Atmospheric Chemistry missions. Other hyperspectral instruments have also been proposed. The ability to validate and characterize the performance of a hyperspectral instrument is a critical aspect of developing and effectively deploying this class of instrument.
With hyperspectral instruments, one of the most difficult and important performance parameters to characterize is the spectral response function (SRF). The SRF is the convolution of the slit response function, the detector, and the spectral response of the instrument. However, systems and procedures for determining the SRF of a hyperspectral instrument have been limited in their capabilities. For example, laser sources have typically been required in order to produce monochromatic energy. However, using lasers as a monochromatic source is difficult where source energy across a wide range of wavelengths is desired. In addition, systems using lasers have only been capable of providing one wavelength of energy to an instrument under test at any one time. Also, lasers produce a point source, so that only one pixel of the instrument under test is illuminated at any one time. As a result of these disadvantages, characterization of an instrument's spectral response function, spectral smile, keystone distortion, and MTF is difficult and inefficient.
Other test systems, in particular the Fourier transform spectrometer, provide a full spectrum of wavelengths simultaneously as a source. However, determining performance characteristics of the system under test requires a large amount or processing, including transforms between Fourier space and instrument space. In addition, signal to noise ratios can be a problem.